Acne is a common skin disorder. Many topical and systemic treatment methods are available (“Handbook of Nonprescription Drugs,” American Pharmaceutical Association, 2002, pages 777-791; Katsambas and Dessiniot, Dermatologic Therapy, 21:86-95, 2008). A major shortcoming of the current treatment methods is their slow response often requiring several months of daily application or administration. Furthermore, satisfactory results achieved are often only about 40% to 60% (Chiou, 2007, U.S. Pat. No. 7,258,875 B2). Multiple (3 to 4) treatment steps are often required. Skin dryness and irritation are common; pitting or scarring may occur after treatment. Serious adverse effects can also occur for potent drugs. Although natural polyvalent metal compounds are recently employed to treat acne (Chiou, 2007, U.S. Pat. No. 7,258,875 B2), the stickiness of products due to the glycerin and thickening agent employed is a major drawback not acceptable by many patients in spite of their efficacy (unpublished observation). This is also the case in treating rosacea (Chiou, 2007, U.S. Pat. No. 7,258,875 B2).
The above review indicates a need to develop a new, cosmetically-acceptable, simple, one-step, highly safe and highly effective method for topically treating acne and rosacea without scarring and pitting. Ideally, the new drug treatment may not require a prescription and the same preparation can be used to treat both disorders. The disclosed embodiments are aimed to achieve the above objectives. This is made possible by a surprising discovery that a commonly used, highly safe and rapidly absorbed (unpublished observation) compound possesses a strong in vitro bactericidal activity against Propionibacterium acnes, that is mainly responsible for the infection in acne. Many other factors are known to contribute to the occurrence of acne and vastly different approaches have been used to tackle the acne disorder. Interestingly, the same compound can also be used to treat infection in rosacea.
Infection-related skin lesions often involve inflammation, redness, swelling, pain, pus formation, itch, irritation, ruptures, wounds, or a combination of any of the above. Infections are caused by microbes, including gram-positive and gram-negative bacteria, viruses, and fungi. Identification of pathogenic microorganisms is preferred prior to anti-microbial therapy (Clinical Dermatology, 2010 by T. P. Habif, Mosby, pp. 454-463). This is because certain microbes only respond to specific antimicrobials. Also, mixed microbes, such as bacteria and fungi, may be present at the same lesion site, hence requiring different antimicrobials for treatment. Emergence of drug resistance further complicates the treatment. In the last several decades, intensive worldwide research has been conducted to discover new topical anti-bacterial, anti-viral, or anti-fungal compounds that are safe in vivo for treating infections; they are different from those compounds used in vitro as disinfectants or for surface sterilization, which do not need to be quickly absorbed, and have lower safety requirements.
It is believed to date that no country has ever approved a compound that can treat topical bacterial, viral, and fungal skin infections, and no single commercial topical product is available that alone can treat these infections. Any new anti-microbial is likely to be expensive and has potential serious, adverse effects. The above discussion indicates a need for an effective, safe, inexpensive compound or composition for killing in vivo a wide variety of bacteria, viruses, and fungi in skin lesions.
Disclosed herein is the surprising discovery that high concentrations of propylene glycol (PG) can be used as a microbicide to effectively treat topical lesions involving bacteria, viruses, and/or fungi (Examples 1-7). Results of in vitro studies (Example 8) appear to support the above contention. PG is relatively inexpensive and is generally regarded as safe by the FDA. PG has been commonly used in the last century in skincare products as a humectant and solvent at generally low concentrations (one to a few percent). It is believed that no commercial product for treating skin infections can show such dramatic killing effect, such as more than 99.9% of microbes killed in less than about one minute. This is significant since many, or perhaps most antibiotics used clinically are not microbicidal; for example, tetracyclines, sulfa drugs, chloramphenicol, griseofulvin, ketoconazole, undecylenic acid, and probably all anti-viral drugs only inhibit microbial growth. Not to be bound by theory, but it is believed that PG may work by disrupting the microbial cell membrane and/or by desiccating the microbes. Thus, the microbes will unlikely develop resistance to PG, an important attribute compared to antibiotics. Another useful attribute of PG is its ability to promote tissue growth and skin firming, as disclosed in U.S. Ser. No. 12/244,924.
Although PG at relatively low concentrations is known as a food preservative that is capable of exhibiting anti-microbial activity (see U.S. Pat. No. 3,853,483), the inventor is believed to be the first to develop and market a commercial product (AcFree Skin™, which contains PG and is covered by U.S. Ser. No. 12/244,924) for use as an effective microbicide to treat any infection-related skin lesions. Past reluctance to use it to treat skin infections may be two-fold. First, there may be perceived notion that PG is poorly permeable across the skin barrier, and hence is ineffective in quickly killing microbes at infection sites. This is because other similar glycols, such as glycerin and ethylene glycol, are known to be poorly permeable. Second, in the last two or three decades, there is a movement to discourage use of PG in skincare; some products are promoted as “propylene glycol free” (See article Propylene Glycol: The Good, the Bad, and the Alternatives by Cathy Sherman, Apr. 30, 2008 posted at http ://www.naturalnews.com/023138_propylene_glycol_food_health.html)
In dermatology, combining active ingredients from two or more drug classes in one product is generally rare. For example, in treating atopic dermatitis or psoriasis, physicians often prescribe a topical steroid for inflammation, a topical antibiotic for infection, a topical antihistamine for itching, and a moisturizer for dryness or scaly skin (Clinical Dermatology, 2010, by T. P. Habif, pp. 171-173, 280-281). Such a multiple-product approach is expensive and inconvenient. Recently, a combined antiperspirant and antimicrobial composition is described (U.S. Pat. No. 7,201,914). A total of 41 antimicrobials are disclosed without specifying their advantages and limitations; for treating skin lesions only one acne example is mentioned. An herbal combination containing five volatile oils to treat a wide range of skin conditions is disclosed in U.S. Pat. No. 7,691,419. The compositions tend to be malodorous and as a result may discourage user compliance.